Does Pain in the Neonatal Period Influence Motor and Sensory Functions in a Similar Way for Males and Females During Post-Natal Development in Rats?

Abstract

OBJECTIVE : Early pain experiences can lead to disruption in the long-term responses to pain and in abnormal development and behavior in rodents. We evaluated the sensory and motor development of Wistar rats after exposure to painful stimulation (repetitive needle prickling) immediately after birth. METHODS : Male and female rats were followed up to 6 months of life, and sensory and motor functions were investigated by testing paw withdrawal with von Frey filaments, calibrated forceps (CF), and grip strength (GS) tests. RESULTS : Body weight increased with age and tended to be smaller in pain groups compared with their controls of the same sex. GS values also increased with age in controls but were stable and even decreased in pain groups from 120 up to 180 days. The von Frey filaments test showed higher values on the nonstimulated paws in male and female pain groups, with no differences between sides on the controls. The CF test showed smaller values on the stimulated paws in the pain group, with no differences between sides on the controls. CONCLUSIONS : Pain in the neonatal period influences sensory and motor functions negatively during development in male and female rats, even long term after the painful stimulus is ceased. The neonatal injury-induced hypersensitivity is persistent, and male and female rats respond similarly to the stimulus.

Substance P in Dorsal Root Ganglion Neurons in Young and Adult Rats, after Nociceptive Stimulation during the Neonatal Period

“…The protocol for the nociceptive stimulation used in our study was adapted from Anand et al (). Our results reproduced those from a previous study in our laboratory where Carmo et al () found no significant differences in body weights between controls and nociceptive neonates at 15 days of life.…”

“…Differences between genders in adult rats of the same age are well described for different rat strains (Sanada et al, ). In an experimental model similar to ours, Carmo et al () also showed that females of the nociceptive and control groups had lower body weight at 180 days than males in the same groups.…”

“…Either on the 15th day after the last stimulation or when the rats reached 180 days of age, von Frey filaments (Semmes‐Weinstein monofilaments—von Frey hairs; Stoelting, Wood Dale, IL), were applied to the hind paw of the rats to test the mechanical allodynia in response to tactile stimulus. The protocol used was that described by Carmo et al (). Briefly, filaments with different bending forces (0.05, 0.2, 2.0, 4.0, 10.0, and 300.0 g) were progressively applied perpendicularly to the plantar region of the hind paw and maintained for 8 s. The lowest bending force at which the rats withdrew their paw for three consecutive applications was recorded as the paw withdrawal threshold.…”

Neonatal pain and stress disrupts later‐life pavlovian fear conditioning and sensory function in rats: Evidence for a two‐hit model

“…The major findings of these studies are that needle pricks, but not inflammation produced a disruption in auditory fear conditioning when collapsed across age and sex, and both needle pricks and nonpainful handling produced a subsequent tactile hypersensitivity in postweaning-aged rats, consistent with a two-hit model of pain susceptibility. Although other studies that have also found effects of neonatal pain and trauma (Carmo et al, 2016;Chocyk et al, 2014), the current work expands upon them by demonstrating the superadditive effects of neonatal pain and later trauma, as well as directly comparing repeated-acute and chronic (inflammatory) pain models.…”

“…Due to the confounding influence of illness or birth complications in humans, preclinical animal studies are often utilized for observing the effects of early life pain. In terms of sensory function, acute neonatal pain produced by two hindpaw pricks per day for the first 15 days of life produced tactile hypersensitivity in rats as old as 180 days (Carmo, Sanada, Machado, & Fazan, 2016). Thermal hypersensitivity has also been observed in 22-day-old rats following four hindpaw pricks per day for the first 7 days of life (Anand, Coskun, Thrivikraman, Nemeroff, & Plotsky, 1999).…”